Potato starch properties by controlled heating in aqueous suspension

ABSTRACT

IMPROVED PASTE AND GEL PROPERTIES AND A HIGHER SWELL ING TEMPERATURE ARE IMPARTED TO POTATO STARCH BY HEATING AN AQUEOUS SUSPENSION OF POTATO STARCH AT TEMPERATURES WHICH ARE AT LEAST INITIALLY BELOW THE NATURAL GELATINIZATION TEMPERATURE OF THE STARCH, BUT ALWAYS BELOW THE HIGH GELATINIZATION TEMPERATURE ATTAINED BY THE STARCH DUE TO SAID HEATING.

United States Paten 3,578,497 POTATO STARCH PROPERTIES BY CONTROLLED HEATING IN AQUEOUS SUSPENSION Erling T. Hjermstad, Cedar Rapids, Iowa, assignor to Penick & Ford, Limited, Cedar Rapids, Iowa No Drawing. Filed May 19, 1969, Ser. No. 826,026

Int. Cl. C131 1 08 U.S.. Cl. 127-32 6 Claims ABSTRACT OF THE DISCLOSURE Improved paste and gel properties and a higher swelling temperature are imparted to potato starch by heating an aqueous suspension of potato starch at temperatures which are at least initially below the natural gelatinization temperature of the starch, but always below the higher gelatinization temperature attained by the starch due to said heating.

BACKGROUND OF THE INVENTION Potato starch when gelatinized in water produces pastes which are highly transparent, glossy, viscoelastic, and non-congealing or gelling on cooling. In higher concentration, or in the presence of other igredients in food formulation, potato starch is apt to produce a very gummy or even slimy texture, and, in the untreated state, has not been particularly suitable for use in certain foods such as starch puddings, salad dressings, canned food thickeners, etc.

Attempts have been made to overcome the pronounced gumminess or sliminess of potato starch pastes by giving the granules a slight degree of cross-linking with chemical cross-linking agents, for example, phosphorus oxychloride, epichlorhydrin, acrolein, divinylsulfone, di-epoxy reagents, aldehydes, glycidaldehyde, thermosetting resins or their monomers, etc. While these are effective in changing the paste character of starches such as a waxy-maize, waxy-milo, or tapioca starch, they have not been particularly effective when used with potato starch. These crosslinking reagents are toxic materials and when any are used in the preparation of food starches, great care must be taken to insure that toxic residual reagents or side reaction products do not remain in the food starch.

Another characteristic of untreated potato starch paste is its extreme susceptibility to breakdown in paste viscosity during cooking or when subjected to the shearing action of agitators, pumps, colloid mills, homogenizers, etc. Chemical cross-linking has been used to stabilize potato starch paste viscosity but it has not proved very elfective with potato starch as compared with the efiect o n starches such as waxy maize or waxy sorghum and also has the considerations of toxicity as indicated above.

Another characteristic of untreated potato starch is its relatively low gelatinization temperature range. Depending on its source and treatment during processing, commercial potato starch tends to irreversibly swell when heated in water at temperatures ranging from 125 F. to 140 F. while commercial corn starch starts to swell in the range of 150 F. to 160 F. This readiness to gelatinize is also manifested in the susceptibility to gelatinization by aqueous alkali at relatively low temperatures. This tendency limits the degree to which potato starch can be monofunctionally etherified with hydrophilic alkyl groups such as hydroxy propyl groups, while retaining filterability and Washability of the starch-ether product.

It has been known for many years that potato starch is particularly susceptible to change in properties when heated at relatively high temperatures in the presence of a limited proportion of moisture insufficient to cause gelatinization. The changes in properties included raising the swelling temperature, increasing paste shortness, opacity and viscosity stability and increasing tendency to congeal and form gels on cooling and ageing. A moderate degree of crystallinity is imparted as shown by X-ray diffraction patterns. While these effects have been known for about 25 years, no commerical application has been made of this effect. This may be due to the unpredictable nature of the process and diificulty in controlling product characteristics.

It is diflicult to uniformly control the heating of large quantities of starch at high moisture content. The moisture tends to concentrate or condense in colder regions or on colder surfaces causing localized starch gelatinization with formation of lumps, balls, flakes, or coatings which contaminate the product. It is also difiicult and power-consuming to agitate or stir large masses of moist starch sufiiciently to transfer heat.

It has now been discovered that potato starch can be given beneficial changes in properties without the use of chemical reagents by warm-water steeping at a pH close to neutrality. Ordinarily, potato starch when used commercially is fairly rapidly heated to its gelatinization temperature and heating is continued to solvate the granules and produce first a suspension of highly swollen granules and then, as the temperature is raised and heating continued, a highly dispersed hydrosol is formed. The present process avoids swelling and gelatinization of the potato starch.

SUMMARY OF THE INVENTION According to the present invention, a concentrated, neutral suspension of potato starch, usually up to about 40% dry substance (d.s.), is first heated for a period of time at a temperature below the incipient swelling temperature of the particular batch of starch being treated. The temperature is then gradually raised until a temperature Well above the original swelling temperature is attained. During subjection to these elevated temperatures the potato starch undergoes progressive changes in prop erties, including raising of its swelling temperature. By this means, swelling temperatures are raised as much as 2030 F. The product after the steeping treatment has a high degree of granule stability. It resists rapid gelatinization and produces a rising or fairly flat viscosity curve on cooling. The pastes of the product are very short textured, non-gummy, non-slimy, cloudy and noncohesive. They form firm gels on cooling and ageing. The changes imparted are produced entirely without addition of chemical reagents and the products are, therefore, ideally suited for uses in food formulation which require short, non-cohesive texture, paste viscosity stability to heat and shearing action, and in foods which require formation of a gel on cooling or ageing.

'It has been discovered that potato starch can be given desirable properties of short, non-cohesive paste texture, higher swelling temperatures, paste viscosity stability, and increased gelling tendency by either a long heating time at a relatively low temperature or by heating short periods of time at successively higher temperatures. Any suspension concentration can be used, providing the suspension is stirrable. Concentrations 20%-40% dry substance are preferred. The pH should be in the neutral range, i.e. about 5.5 to 8.0, especially if acid degradation or alkaline swelling or oxidation is to be avoided. A pH in the range of 6.(l-7.5 is preferred.

It is essential that swelling be avoided during the different heating periods; otherwise, higher temperatures will cause the suspensions to gelatinize to an unstirrable, sticky, non-dewaterable state, especially in higher solids suspensions.

Commercial potato starches vary considerably in their gelatinization temperature ranges. Generally, when a susa pension of potato starch is cooked or gelatinized under normal cooking procedures it starts to swell wtihin a temperature range of 130 to 140 F. However, occasionally some batches have been found to swell at lower temperatures, for example at 125 F. It is, therefore, preferred in the present process to heat the suspension at an initial temperature of 120 F., though for some batches higher initial temperatures have been used without causing swelling. Each temperature level of heating must be below the original swelling temperature or the swelling temperature attained by the present process.

Swelling temperature or gelatinization temperature can be determined by any of several methods; for example, observing loss of birefringence of the granules under a microscope while raising the temperature, observing the changes in translucency of suspensions, changes in refractive index on heating, or changes in viscosity on heating. It has been found, however, that a relatively simple test is sufliciently accurate to characterize starches for the present process. The test is conducted by agitating a 40% dry substance suspension of potato starch in water at pH 6.5 with a propeller, raising the temperature at about 1 F. per minute and noting the temperature at which the suspension thickens and the vortex created by the propeller disappears. Normal commercial, unmodified potato starch swells between 130 and 135 F. by this test.

In many food formulations, such as salad dressings, canned foods, pie fillings, soup thickeners, etc., untreated potato starch imparts a gummy or slimy texture which is undesirable. By a suitable degree of heating of a water suspension, potato starch can be given varying degrees of paste shortness or decreased paste conhesiveness to make it suitable in consistency for such food uses. Sufiicient gelling tendency can be imparted by the present process DESCRIPTION OF PREFERRED EMBODIMENTS Example 1 The purpose of this example is show the effect of prolonged heating of the starch suspensions at difierent temperature levels.

Unmodified potato starch (commercial starch from Idaho potatoes) was suspended in water in 40% dry substance concentration and the pH of the suspension adjusted to 6.5. Several such suspensions were heated and agitated gently at different temperature levels for at least 20 hours. Before and after the heating period the swelling temperature was determined by agitating a 40% d.s. suspension with a propeller, raising the temperature at around 1 F. per minute and noting the temperature at which the vortex disappears and the suspension becomes semisolid and unstirrable.

The above data show the effect of suspension heating in raising the swelling temperature.

4 Example 2 .This example shows the elfect of increasing time of heating at a single temperature level.

Commercial unmodified potato starch was suspended in Water in a 40% d.s. concentration at pH 6.5 and agitated at 125 F. for varying periods of time. Swelling temperatures were determined before heating and after each time period by the method in Example 1.

Swelling tem- Time heated at 125 F.: perature, F.

None 130 3.5 hrs. 1'42 5 hrs 143 6 hrs 145 17 hrs 147 Example 3 and the swelling temperature determined after the final heating. The results are given below.

Hours Swelling Temperature heated, F temp l 40 min. (swelled).

The above data show that a potato starch which swells at 125 F. without pre-treatment can be modified by heating to resist swelling when heated in suspension at temperatures as high as 140 F. No thickening of the suspension occurred at these elevated temperatures. The starch remained in the native, unswollen granule form and was readily filterable and Washable without swelling after the heating treatment.

Example 4 The data in this example show the eliect of suspension pH on the change in properties of potato starch during suspension heating according to the present invention.

Unmodified commercial potato starch having a swelling temperature of 133 F. as determined in Example 1 was suspended in water in 40% dry substance concentrations. The pH of each suspension was adjusted with a slight amount of HCl or NaOH. The suspensions were heated at diiterent successive temperature levels as follows.

Degrees F.: Hours 120 1 130 2 135 3 140 2 The swelling temperatures attained at the different pH levels were determined.

Swelling temperature after pH: final heating, F. 5 5 143 60 147 6 5 151 7.0 150 7.5 149 8.0 (Swelled after 1 hr. at 140 F.)

The above data show that the greatest effect on the TABLE H starch is obtained at about a neutral condition, i.e., pH in the range of 6.0 to 7.5. Heatmg Example i N096,

The data in this example show that there is no diiference 5 2 133 i jis iiis. in effect of heating at a low temperature for along period gi fhr of time in demineralized water and in water of medium 3 130 F'.1 hr hardness. 235 hrs Unmodified commercial potato starch was suspended 120 F.'-'1 hr. in 40% d.s. concentration in water which had been de- 4 13 mineralized by pouring through ion exchange units and U 140 F92 hrs: in water of 5 grains per gallon hardness. The pH of the ff' hm suspensions was adjusted to 6.5. The suspensions were 130 F.2 hrs. heated at 120 F. for 18 hours, then dewatered and the 5 53: starch dried at room temperature. These starches and the 1 I untreated base starch were compared by cooking in a $80 .1 5, Corn Industries Viscometer in 5% dry substance concen- 6 135: F.3 hrs. tration for 30 minutes with a water bath temperature of hrs 210 F. The pastes from the Cl. viscometer runs were used for preparing gels for testing with a Corn Industries 7 13,

Gelometer and for Brookfield viscometer viscosity (20 8 120F.-1hr.' r.p.m.) at temperature levels of 190 F., 150 F., and

TABLE III 0.1. viscometer-5% d.s. concentration- 210 F. bath-pH 7.0

Temp. Time Peak 30, Brookfield (20 r.p.m.)

initial to viscosviscos- Gel, centipoise visreach ity ity 24 hr., cosity, peak, (g. 68 F. 190 150 120 F. min. cm.) cm.) (gram) F. F. F. Aged paste 144 2, 040 400 9 2, 600 3, 000 4, 150 Clear, slimy. 172 20 1, 035 900 100 8, 100 900 9, 700 Cloudy, gelled. 175 21 1, 080 990 110 10, 100 12, 000 13, 500 D0. 175 828 792 115 8,500 9,700 9,700 Cloudy, noncohesive. 174 20 1,125 990 130 9,050 10,300 11,400 Cloudy, gelled. 178 25 900 855 130 8,650 9,800 11, 000 Do. 172 25 876 860 145 8,600 9,200 10,100 Do. 180 680 680 210 7, 300 9,000 11,400 Do.

120 F. The above instruments and their use are described The abve data 111 Table III show the raising of swelling in Methods in Carbohydrate Chemistry: vol. IV, by R. L. temperature (temperature initial viscosity) as compared Whistler, Academic Press, New York, 1964, pp. 117-121, with that of untreated potato starch, as the time and 148-150, and 121-123, respectively. The results obtained temperatures of treatments are increased. Peak viscosities are shown in Table I. are considerably lowered and the pastes resist viscosity TABLE. I

0.1. viscometer, 5% d.s. concentration, 210 F. bath, pH 7.0

Temp. Peak Gel, Brookfield (20 r.p.m.)

initial vis- 30' vis- 24 hr., centipoise viscosicosity, cosity, 68 F., Suspenslon heating conditions ty, F. g. cm. g. cm. g. 190 F. 150 F. 120 F. Aged paste None (control) 144 2, 040 400 9 2, 600 3, 000 4, 150 Clear, slimy. 120 F., 18 hr., demineralized 13120--" 155 1, 260 630 26 6, 000 7, 000 7,600 Slight cloudy. 120 F., 18 hr., H2O medium hardness 155 1, 080 612 30 6, 400 7, 100 7, 700 Do.

The above data show that water hardness does not afbreakdown, as indicated by the high values obtained after feet the changes in swelling temperature and viscosity 30 minutes of continuous shearing agitation at high temcharacteristics of the product. Similar values are obperatures. Gel strengths of the pastes are substantially intained using either medium hardness or ion free water. creased as well as Brookfield viscosity, especially on cool- Heating at the low temperature of 120 F. produced coning to lower temperatures.

siderable improvement in the viscosity and gel character Having described the invention, what is claimed is:

of the potato starch, 1. A process for treating potato starch to eifect an ini crease in the swelling temperature and improve the paste Exampk 6 and gel properties of said potato starch while maintaining The fi t of heating potato Starch Suspensions under said potato starch in the substantailly unswollen native varying conditions for different time Pmiods are Shown granule state, wh ch process comprises forming a stumble in this 1 aqueous suspension of potato starch granules at a pH Potato Starch Suspensions were d up as in Example 1n the range of about 5.5 to about 8.0 and maintaining the 5, using water of medium hardness. Heating temperature, temperature of Said Suspension below Swelling time, and pH were varied. The starches after heating were perature of the Starch and above about for a t dewatered, dried at room temperature, and compared us of at least about one hour, which time is Suificiellt i0 ing the Corn Industries viscometer, Corn Industries cause an increase in the swelling temperature of said pogelometer, and Brookfield viscometer as in Example 5. tato starch. The suspension heating conditions for the various tests 2. The process of claim 1 wherein the temperature of are shown in Table II. Properties of the starches produced said suspension is first maintained at a temperature of in the tests are shown in Table III. about 5 to 10 F. below the swelling temperature of said starch for about 1 hour and then gradually increased to about 140 F.

3. The process of claim 1 wherein the pH of said suspension is maintained in the range of about 6.0 to about 7.5.

4. The process of claim 1 wherein the temperature of said suspension is gradually raised to above the natural swelling temperature of the starch but below the swelling temperature attained by the starch due to said heating,

and maintaining the starch during said heating in a readily 10 filterable, substantially unswollen, native granule state. 5. Potato starch in the substantially unswollen native granule state which has been treated according to the process of claim 1.

6. A process for increasing the swelling temperature of potato starch while maintaining said potato starch in the substantially unswollen native granule state, which process comprises forming a slurry of potato starch granules in Water, heating said slurry to a temperature in the range of about 100 to 125 F. and maintaining said slurry at said temperature for at least one hour.

References Cited UNITED STATES PATENTS 2,332,320 10/1943 Kerr 12771 3,300,316 1/1967 Cooper 99139X MORRIS O. WOLK, Primary Examiner S. MARANTZ, Assistant Examiner US. Cl. X.R. 

